Polymer particles are widely used as coating, adhesive, ink and painting materials, for precision mold constructions and the manufacture of micro-sized materials. The unique properties of micro- and nanoscaled polymer particles with low polydispersities have meanwhile gained significant attention not only in the electronics industry, for example, in the manufacture of TFT and LCD displays, digital toners and e-paper, but also in the medical sector such as for drug delivery systems, diagnostic sensors, contrast agents and many other fields of industry.
Polymer nanoparticles are frequently synthesized by physical methods such as the evaporation of polymer solution droplets or by the direct synthesis of the nanoparticles using special polymerisation processes. The most common processes are radical polymerisations such as suspension polymerizations and emulsion polymerizations.
Over the last decades, a number of radical polymerization processes were developed in order to achieve a better control over the polymerisation process and thus the properties of the resulting polymer nanoparticles.
S. Nozari et al. (Macromolecules 2005, 38, 10449) describes a RAFT (reversible addition fragmentation transfer) emulsion polymerization process for the preparation of polystyrene nanoparticles using dithioic acids as sur-iniferters, thereby obtaining polystyrene with an polydispersity index (Mw/Mn), hereinafter also referred to as M-PDI, of 1.22 to 1.31, and a weight average molar mass of 110 to 170 kg/mol.
Emulsion polymerisations induced by X-ray radiation are described in S. Wang, X. Wang, Z. Zhang, Eur. Polym. J., 2007, 43, 178.
Emulsion polymerisations induced by UV/Vis radiation are described in P. Kuo, N. Turro, Macromolekules 1987, 20, 1216-1221, wherein the formation of polystyrene nanoparticles having a M-PDI of 1.6 to 2.2 and a weight average molecular weight of 500 kg/mol or less.
The industrial applicability of the processes described above is, however, hampered due to the use of toxic, expensive, coloured or malodorant chemicals such as heavy metal salts, sulphur containing compounds and stable radicals such as 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO).